Is it ok for children to hear parents having ?

For example, we put the kids to bed and think they are sleeping. We shut our bedroom door and lock it, and in the middle of our (time) we hear footprints running away from our door! Or in the middle of the day if we have the kids watch tv or something while we come in the room for a little while, lol. I hate feeling that my daughter might have a clue what we are doing, and he says its ok and its normal. They are 10yr old-girl and 4yr old -boy Pls let me know what you think